1. Field of the Invention
The present invention is an improved thin-film magnetic head device, specifically a thin-film magnetic head modeled after thin-film magnetic heads which reproduce digitally recorded signals from magnetic tape.
2. Description of the Related Art
Conventional pulse code modulation (PCM) devices used to reproduce pulse-coded modulation signals recorded on multiple tracks require many electronic-circuit components in the periphery of the magnetic head assembly unit. FIG. 1 shows a typical example of a conventional device used to reproduce PCM signals recorded on multiple tracks. The PCM signals recorded on magnetic tape 1 are reproduced by the playback head 2, and are then amplified to the needed level by amplifier circuit 3. The amplified PCM signals are then subjected to waveform equalization by the waveform equalizer circuit 4 after which they are sent to level detection circuit 5 and then converted into digital pulse signals by decoding circuit 6. This digital information is then input to the digital signal processing circuit 7, where it is demodulated and subjected to phase correction. These demodulated signals are then converted to analogue signals by D/A converter 8 and output at audio signal output terminal 9.
Thus, in the device shown in FIG. 1, it is necessary to have a number of circuits following amplifier circuit 3 to correspond to the number of tracks present in the tape. Taking this into account, one arrangement proposed in the prior art had a circuit format in which a number of circuits are inserted between tracks so that the number of circuits can be reduced to a minimum. FIG. 2 denotes a typical circuit configuration found in one of the prior art arrangements. FIG. 2 is a block diagram of circuits in the periphery of the magnetic reproducing head used to execute a time-sharing process. In this process, constant-current source 10 delivers constant current to the yoke-type magnetic resistor (YMR) 11 (in this case the reproducing thin-film magnetic head itself), and as a result, a specific voltage signal is generated by the varied magnetic resistance. A high-pass filter composed of capacitor 12 and resistor 13 filters out the DC components, and the resultant AC signal is then amplified by amplifier circuit 3. These AC signals, reproduced and amplified by multiple tracks, are then selected in sequence by analogue multiplexer 14, and converted again into digital signals by A/D converter 15. These digitalized signals are then processed by digital waveform equalizer circuit 16 to eventually generate signal 17.
Nevertheless, as shown in FIG. 2, even when the time-sharing process is executed, the conventional configuration still includes by necessity those circuits ranging between the yoke-type magnetic resistor (yoke-type magnetic head) 11 and the signal switching circuit 14. In other words, circuits corresponding in number to the number of tracks are needed. Conventionally, those circuits beyond the constant-current source 10 and capacitor 12 are located outside the casing of the magnetic head 11 (YMR), and these circuits are connected to each other by means of wires on a flexible printed circuit board (hereinafter called FPC). This high number of circuit wires degrades the quality of the signals due to the number of tracks, an extremely minimal level of output signal, and a poor signal-to-noise (S/N) ratio. A high data error rate results, hampering adequate use.
FIG. 3 is a sectional view of one conventional magnetic head assembly. In FIG. 3, yoke-type magnetic resistance is generated inside ferrite substrate 21 and protection glass 20. To strengthen protection and increase magnetic shielding, the magnetic heads are mounted inside metal casings 18 and 19. Connection between the magnetic heads and the external reproducing circuits is achieved by bonding said flexible printed circuit board 23 with metal casing 19. Magnetic head and flexible printed circuit board 23 are connected by wire and or other form of wire 22. The magnetic heads are connected in turn to external circuits by means of the flexible printed circuit board. Space inside metal casings 18 and 19 is filled with molded resin 32. The conventional head-installation method described above could potentially generate many errors due to low output signals and a poor S/N ratio for all data. This unwanted phenomenon as mentioned earlier, increases in proportion to the number of tracks in the tape, thus resulting in critical problems in actual use.